It is known that DHNA is useful as an industrial material, for example, for dyestuffs, pigments, sensitive materials and the like, and various synthesizing methods thereof according to organic chemical syntheses have been reported (refer to, for example, JP-A-57-128655, JP-A-59-186942 and JP-A-60-104037). Since the aforementioned methods require a reaction in an organic solvent under high temperature and high pressure, or use of a reagent or the like which is not suitable for eating and drinking, as the catalyst or the like, DHNA obtained by such methods have not been employed in food and drink or pharmaceuticals.
Accordingly, the present inventors have carried out a study on an alternative method thereof, and found a method for producing DHNA in a large amount intracellularly and extracellularly by using the bacterium belonging to the genus Propionibacterium. Thereafter, it was found that the DHNA-containing composition obtained from this culture mixture, or DHNA or a salt thereof, is useful for the prevention, treatment and the like of metabolic bone disease, since it has the actions to improve intestinal flora and to reduce the abdominal discomfort symptom appeared in milk-sensitive patients at the time of milk ingestion, and further accelerates differentiation and functional expression of osteoblast and inhibits formation of osteoclast (refer to WO 03/016544 A1).
However, when a culture of the bacterium belonging to the genus Propionibacterium is applied to food and drink or pharmaceuticals as a food material for the purpose of adding the physiological function possessed by DHNA, there is a disadvantage that the residual amount of DHNA is considerably reduced during the production and storage thereof. For example, it is known that ascorbic acid, hyposulfurous acid and/or acetic anhydride is/are used for the stabilization of Bifidus factor contained in the culture mixture of the bacterium belonging to the genus Propionibacterium (refer to JP-A-10-108672). However, there are the outstanding problems in employing this method that the original taste of food and drink are impaired, or the substances cannot be used since they are not recognized as food additives, and the like.